"My Esperanto" is surely an English idiom, meaning, "My ability in Esperanto"
Ne plu ol iu de ni, Jo.
Plibonas just means "is better" (estas plibona) and if the sentence was "My Esperanto is better." it would leave us asking "than what?" Or, it would be because you saw someone else's Esperanto and saw a great many obvious, to you, errors in it.
The other forms of the word are well enough covered above that I don't need to repeat them.
Mi estas denaska angla parolanto. When I see a sentence like you wrote here I know that English is, at least, your second language. (nothing to be ashamed of, many native English speakers hardly know more than a word or two of another language.) As Crlight said, it's technically correct, but it shows room for improvement. Keep improving and someday you may be among the best.